Recently upgraded our Enterprise deployment in steps from 10.6.1 to 10.8.1 to 11.1.
At 11.1, our Portal Homepage shows no Contents, though the expected folders are still visible.
All of our Services (accessible via the Server Homepage) are still there, and apparently running.
The Portal Administrator Directory's Index Status usually returns 0 for Indexed Items:

And anything I do to remedy the situation is for naught, because running Reindex from Portal Admin results in zeroing the index again.
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What I've tried so far:
Visit the ArcGIS Portal Directory, where all of the items I expect to see in the Portal Home are present, if a bit difficult to use.
- Select an item from a folder, Update Item without making any updates.
- It appears in the Portal Homepage Contents. Portal Admin's Index Status shows it in the Index count.
- Reindex from Portal Admin --> Vanishes from Portal Contents
- Select an item from a folder, Update Item without making any updates.
- It appears in the Portal Homepage Contents
- Use ArcGIS Pro to "Overwrite Web Layer" -effectively updating the Service, and interacting with the Portal Content item
- Reindex from Portal Admin --> Vanishes from Portal Contents
- Publish an entirely new Web Layer. Item appears as an active Service, and has a Portal Content Item.
- Reindex from Portal Admin --> Vanishes from Portal Contents
- Replace the working arcgisportal content items folder with the one added as a template in the installation files. ...Restarting the Portal Service.
- Index Status starts at 0; Reindex does nothing to change that status.
It is clear to me that Portal Admin's "Reindex" tool isn't working as intended. I want to know why, and how I can fix it. Any ideas?
Our Server is Federated.
PS: If for any reason our Portal Service is Restarted, some Service Items do not [re]appear in Maps that utilize them... though the Services themselves still run. My temporary remedy to this is to go through the steps in blue text (above), which appears to resume normal Service services -even after another reindex operation is attempted.